Both baking soda and baking powder are leavening agents, which means that when they are combined with other ingredients in a batter or dough, they react to create carbon dioxide gas, which escapes from the batter and lifts it along. We may thus conclude that both contribute to the rising of cakes and other baked goods.

Usually, baking powder is used to make cakes, however baking soda can also be used on occasion. But both the preparation and the flavour of the finished cake are affected by this.
The cake has a somewhat bitter flavour when baking soda is substituted for baking powder. Carbonate of sodium is what makes up baking soda. This turns into sodium carbonate, which has a harsh flavour, when heated. The result of the reaction is;

$2{\mathrm{NaHCO}}_3\stackrel{\text{ Heat }}{⟶}{\mathrm{Na}}_2{\mathrm{CO}}_3+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$

However, baking soda and tartaric acid can be combined to create baking powder in the proper proportion. When tartaric acid is added, the sodium carbonate that results from the breakdown of sodium hydrogen carbonate is neutralised, preventing the cake from tasting even more bitter.
Tartaric acid balances the medium as a result of its addition.

Hence, the correct option is (C).